You would want to avoid most synthetic materials in a hot climate (with a few exceptions). Synthetic materials don't "breathe." Worse, some absorb and trap heat which is a common complaint.

I would say look for something made from all natural latex. Latex has very unique characteristics. It's not temperature sensitive and it's quite breathable. It has great longevity and gives great support as well. Look for one that is wrapped in organic wool. Believe it or not, wool has an amazing ability to regulate temperature and has been used for hundreds of years because of this. Keeps you cooler when it's hot and warmer when it's cold. Also look for a 100% cotton cover or bamboo cover as both are very breathable. The combination of these natural materials work synergistically together to create an even climate for you at night.

One exception would be for something that uses a ton of cooling gel in the mattress rather than a "gel infused" mattress. For example Technogel makes a great memory foam mattress that uses a thick layer of gel on the surface, and you can actually feel the "coolness" of it and the effect lasts a while. I've tested one of their models out and I was impressed at how well it worked.

There's some promising advancements with PCM (phase changing material) out there in some models such as Outlast that work "ok." I predict the technology will improve over time. But really, I don't think anything can hold a candle to natural fibers and organic materials. Some may disagree with me. ;-)

Sean

I agree with Sean here that natural materials are generally better. A couple other things to consider:

• Many types of memory foam are very sensitive to heat, so they can soften up significantly in a hot climate -- this could be either a great thing or a terrible thing, depending on your preferences
• If you are sensitive to getting hot while you sleep, you probably want to avoid mattresses that allow you to sink "in" to the bed, and focus more on ones that you sleep "on". All else being equal, the more of your skin that is in contact with the air, the cooler you'll feel.

There are some interesting developments on the foam front, check out the Gemma Mattresses from Spaldin. I started importing these from Spain. Nothing like them in the USA. 60% natural plant oil, non-GMO, extremely durable foam and also extremely porous, with an organic cotton cover, affordable and breathable. Yes, latex and natural beds are very cool sleeping as well, but for $999 queen and Oeko Tex Certified, its hard to beat the Gemma.

It's not so hard to beat the Gemma. Natura, a Canadian based company, offers a natural plant based core mattress, with 2" of natural Talalay Latex and a wool top with a cotton cover for only $1,149 in queen...less 10% off if you order on-line.

Pete

The best? A hammock. You want something that does not retain heat. Most foams will. In order to compensate, there are items in the market to help cool the mattress. Chili technologies makes one, as does Sleep Number. These are additives to the surface to cool them off. Using these would allow you a broader range in mattresses. Keep in mind that these products would affect how foams react under them, especially heat sensitive memory foam. Also, there is an old trick that works well in dry heat, but that is to mist your top sheet with water then drape the foot over a fan at slow speed, this will act like air conditioning. Depending on your location though, A/C is your best bet.